Another "myth to kill"??.....what makes it go???

[AKKAMAAN]

There is something wrong with above equation.

I can agree one this one.....:thumbsup:

 

[gpflepsen]

Head pressure or pressure from a prime mover powered pump does not matter PRESSURE=PRESSURE



Please back this one up!!
In metric system I'll tell you what you just said....
Flow unit = m3/s
Pressure unit = N/m2
Friction or resistance is equal to force, actually opposing force...unit=N

Never said I was using SI units. The equation is a generality. Flow is proportional to pressure. The unit of resistance would have to be in terms that made sense. Actually, the units of resistance would be N-s/m^5 for this situation.

so here is your equality, and I'll simplify it for you too

m3/s =(N/m2)/N
simplified step 1
m3/s=1/m2
simplified step 2
m3 x m2 x s/s = m2/m2 x s
simplified step 3
m5=s
"m5" equals time???????

Everything cancels out, 1=1.

:confused2::confused2::confused2:

Come back after you have "backed up" that formula statement

A simple example of the above equation, although in the electric domain, would be:

Current = voltage / resistance; or V=IR

The units of resistance is volts/amps.

And Redneck, if pressure increases, flow will have to increase. Think of the electric analogy. If you increase the voltage, the current will increase. That's known as Ohm's Law.

For hydraulics, the pressure is usually proportional to the flow squared and is not a linear relationship. P=C x Q^2

Does that "back up" my formula statement? :confused2:

All I am saying is that two different hydraulic situations can be modeled, one in which pressures are an input and one where flows are the input. The resulting motions, pressures and flows are dependent upon the reactions to the inputs. And yes, Newton was also correct.

 

[mmurphy]

Hey, this is getting interesting!!!!:thumbsup:
The metric stuff is a little hard on my poor little marble!

 

[Redneck in training]

Pressure=Resistance/Flow
N/m2=N/(m3/s)
Simplified step 1
m3 x N/m2 /(N)=N x m3/(N x m3/s)
Simplified step 2
m = s
"distance" equals "time"?????

Nope that didn't work either....back to class.....:laughing:

Perhaps the relationship is more complicated but I tried conveying that if the pump delivers constant flow then the resistance will affect both flow and pressure in opposite manner. In example: Resistance rises, pressure rises, and flow goes down and vice versa. Like in Ohm law. Since the hydraulic system has energy loss the equation perhaps should be Pressure=Resistance/Flow*efficiency coefficient.
Hydraulic power=Flow*pressure*efficiency.
What makes hydraulic system work is ability of the pump to deliver certain flow while maintaining certain pressure. In theory any size of the pump will make hydraulic cylinder/motor work but it might be very slow on one extreme or uncontrollably fast on the other.

 

[J_J]

I know you guys are exercising your brain power, but most of us only know how to turn a wrench.

You can have lots of flow, and no or little pressure. Not much work can be done here. Just a little flow, and max pressure caused by high resistance will accomplished the designed work.

 

[AKKAMAAN]

Never said I was using SI units. The equation is a generality.

Does not matter what units you use....it will come out the same way.....
You stated that "Flow=Pressure/Friction"

Flow=volume per time unit
Volume is distance x distance x distance=distance^3, common std unit is inch, so it will be inch^3
Time is measured in seconds, s.
Pressure is force per area unit
Common std unit for force is pounds, lbs.
Area is distance x distance=distance^2, common std unit is inch, so it will be inch^2
Friction is a force that is opposing the a the force that tries to move an object.

Your statement "Flow=Pressure/Friction" can be expressed like this...
volume/time=(force/area)/force
or
inch^3/s=(lbs/inch^2)/lbs
and it will come out as
inch^5=s.......:thumbdown:

Flow is proportional to pressure.

proof it or take it back!!

The unit of resistance would have to be in terms that made sense. Actually, the units of resistance would be N-s/m^5 for this situation.

Don't go public with that one....LOL....:thumbdown:

Everything cancels out, 1=1.

Did not! :thumbdown:

A simple example of the above equation, although in the electric domain, would be:

Current = voltage / resistance; or V=IR

The units of resistance is volts/amps.

I love hydraulic-electric analogies!:thumbsup:
But they have to be used carefully, a std electric system is almost always constant pressure (voltage) and closed loop. I just dont see how electric analogy will save your day here.....the amps is flow and the voltage is the pressure, the resistance is the load........it is the voltage that drives the amps through the circuit. Voltage is the "force".....force makes it, the amps, go.

And Redneck, if pressure increases, flow will have to increase.

I am OK with that!

Think of the electric analogy. If you increase the voltage, the current will increase. That's known as Ohm's Law

.
I am OK with that too!

For hydraulics, the pressure is usually proportional to the flow squared and is not a linear relationship. P=C x Q^2

Does that "back up" my formula statement? :confused2:

I am confused too....:confused2:

All I am saying is that two different hydraulic situations can be modeled, one in which pressures are an input and one where flows are the input. The resulting motions, pressures and flows are dependent upon the reactions to the inputs. And yes, Newton was also correct.

If we use a combustion engine, the source for the prime mover force is in the combustion room, converted from chemical energy stored in fuel and oxygen. The rest of the drive chain can be considered part of the load, piston, crankshaft, pump shaft, gears, fluid, piston, piston rod,linkage and finally "the bucket", that lift the load.
Flow is just something that happens (action or reaction) in the drive chain.....flow is just moving fluid....like the moving piston rod.....but just because the fixation that hydraulics is "complicated", we think that flow is magic.....no one ever calls that the "flow" of piston rod "makes it go"...inch^3 per second of solid steel.....which is an equivalent call to that "flow makes it go".....

Myth dead now?

ps. Glad you accepted that Newton was correct!!:thumbsup:

 

[AKKAMAAN]

Perhaps the relationship is more complicated but I tried conveying that if the pump delivers constant flow then the resistance will affect both flow and pressure in opposite manner.

If there is a constant flow, how can resistance affect flow other than if some flow gets diverted through PRV or internal/external leakage??

In example: Resistance rises, pressure rises, and flow goes down and vice versa. Like in Ohm law.

You just stated flow was constant.

Since the hydraulic system has energy loss the equation perhaps should be Pressure=Resistance/Flow*efficiency coefficient.

If you try to make the analogy with Ohm's law the formula would be Pressure=Resistance x Flow or Flow = Pressure/Resistance

Hydraulic power=Flow*pressure*efficiency.

OK!

What makes hydraulic system work is ability of the pump (and the prime mover) to deliver certain flow while maintaining certain pressure. In theory any size of the pump will make hydraulic cylinder/motor work but it might be very slow on one extreme or uncontrollably fast on the other.

OK! too...

 

[Egon]

Everybody bored today with nothing useful to do?:laughing:

Just remember water runs downhill and you can't push on a rope and all will end well.

And when a line breaks there's usually a mess regardless of units!:thumbsup:

 

[dcyrilc]

Everybody bored today with nothing useful to do?:laughing:

Just remember water runs downhill and you can't push on a rope and all will end well.

And when a line breaks there's usually a mess regardless of units!:thumbsup:

Yea, yea, yea... you had to remind me that I have a loader line leaking, didn't ya?:laughing:

How you doin' tonight Egon?

 

[kennyd]

Everybody bored today with nothing useful to do?:laughing:

Just remember water runs downhill and you can't push on a rope and all will end well.

And when a line breaks there's usually a mess regardless of units!:thumbsup:

You can't nail Jello to the wall either:laughing: